From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 36486C4332F for ; Thu, 3 Nov 2022 16:38:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232271AbiKCQii (ORCPT ); Thu, 3 Nov 2022 12:38:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60410 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232363AbiKCQiT (ORCPT ); Thu, 3 Nov 2022 12:38:19 -0400 Received: from mx.cjr.nz (mx.cjr.nz [51.158.111.142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9C0D21DA72; Thu, 3 Nov 2022 09:35:06 -0700 (PDT) Received: from authenticated-user (mx.cjr.nz [51.158.111.142]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-384) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: pc) by mx.cjr.nz (Postfix) with ESMTPSA id 9F6BC7FC21; Thu, 3 Nov 2022 16:34:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cjr.nz; s=dkim; t=1667493261; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=L7oeyOE9y+SCE0Fp1mehfx0R2Rb8YrWpiTFfBzwVnbE=; b=A/1/IKG1KpNtZhg+9WqvL6/jgQa6rGajHLy3ic5Bme0VfEK1IHzSnukadQAEuBZ28Gu7+B 8jiA1IiBGxC9W2ymqpOFxlp7g/ckpa+u+bCDt+5XnsJBUqo15qEKdMh9WmvqcFHfOwlcl1 xardnrPb3Ah1qZ08IIbGaDHIctH5rlEfe05yvHZwLscMCxQJMomFFQgAuezfaQXgaejG5+ vTyzkQJYiCFgpfeZGEHea0YMGv/tlGvzdR3J6orRmax8in0OnE0cjzzRHlDu5UiF5hYSXa PYuHrPtSGMTP1WlYRpMn4KTytQjHAugGjUGlKcmE3dCATYu1POmvpeCKgsQhUA== From: Paulo Alcantara To: ChenXiaoSong , sfrench@samba.org, lsahlber@redhat.com Cc: linux-cifs@vger.kernel.org, samba-technical@lists.samba.org, linux-kernel@vger.kernel.org, chenxiaosong2@huawei.com, yi.zhang@huawei.com, zhangxiaoxu5@huawei.com Subject: Re: [PATCH] cifs: fix use-after-free on the link name In-Reply-To: <20221102061659.920334-1-chenxiaosong2@huawei.com> References: <20221102061659.920334-1-chenxiaosong2@huawei.com> Date: Thu, 03 Nov 2022 13:35:30 -0300 Message-ID: <875yfw0ze5.fsf@cjr.nz> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-cifs@vger.kernel.org ChenXiaoSong writes: > xfstests generic/011 reported use-after-free bug as follows: > > BUG: KASAN: use-after-free in __d_alloc+0x269/0x859 > Read of size 15 at addr ffff8880078933a0 by task dirstress/952 > > CPU: 1 PID: 952 Comm: dirstress Not tainted 6.1.0-rc3+ #77 > Call Trace: > __dump_stack+0x23/0x29 > dump_stack_lvl+0x51/0x73 > print_address_description+0x67/0x27f > print_report+0x3e/0x5c > kasan_report+0x7b/0xa8 > kasan_check_range+0x1b2/0x1c1 > memcpy+0x22/0x5d > __d_alloc+0x269/0x859 > d_alloc+0x45/0x20c > d_alloc_parallel+0xb2/0x8b2 > lookup_open+0x3b8/0x9f9 > open_last_lookups+0x63d/0xc26 > path_openat+0x11a/0x261 > do_filp_open+0xcc/0x168 > do_sys_openat2+0x13b/0x3f7 > do_sys_open+0x10f/0x146 > __se_sys_creat+0x27/0x2e > __x64_sys_creat+0x55/0x6a > do_syscall_64+0x40/0x96 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > Allocated by task 952: > kasan_save_stack+0x1f/0x42 > kasan_set_track+0x21/0x2a > kasan_save_alloc_info+0x17/0x1d > __kasan_kmalloc+0x7e/0x87 > __kmalloc_node_track_caller+0x59/0x155 > kstrndup+0x60/0xe6 > parse_mf_symlink+0x215/0x30b > check_mf_symlink+0x260/0x36a > cifs_get_inode_info+0x14e1/0x1690 > cifs_revalidate_dentry_attr+0x70d/0x964 > cifs_revalidate_dentry+0x36/0x62 > cifs_d_revalidate+0x162/0x446 > lookup_open+0x36f/0x9f9 > open_last_lookups+0x63d/0xc26 > path_openat+0x11a/0x261 > do_filp_open+0xcc/0x168 > do_sys_openat2+0x13b/0x3f7 > do_sys_open+0x10f/0x146 > __se_sys_creat+0x27/0x2e > __x64_sys_creat+0x55/0x6a > do_syscall_64+0x40/0x96 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > Freed by task 950: > kasan_save_stack+0x1f/0x42 > kasan_set_track+0x21/0x2a > kasan_save_free_info+0x1c/0x34 > ____kasan_slab_free+0x1c1/0x1d5 > __kasan_slab_free+0xe/0x13 > __kmem_cache_free+0x29a/0x387 > kfree+0xd3/0x10e > cifs_fattr_to_inode+0xb6a/0xc8c > cifs_get_inode_info+0x3cb/0x1690 > cifs_revalidate_dentry_attr+0x70d/0x964 > cifs_revalidate_dentry+0x36/0x62 > cifs_d_revalidate+0x162/0x446 > lookup_open+0x36f/0x9f9 > open_last_lookups+0x63d/0xc26 > path_openat+0x11a/0x261 > do_filp_open+0xcc/0x168 > do_sys_openat2+0x13b/0x3f7 > do_sys_open+0x10f/0x146 > __se_sys_creat+0x27/0x2e > __x64_sys_creat+0x55/0x6a > do_syscall_64+0x40/0x96 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > When opened a symlink, link name is from 'inode->i_link', but it may be > reset to a new value when revalidate the dentry. If some processes get the > link name on the race scenario, then UAF will happen on link name. > > Fix this by implementing 'get_link' interface to duplicate the link name. > > Fixes: 76894f3e2f71 ("cifs: improve symlink handling for smb2+") > Signed-off-by: ChenXiaoSong > --- > fs/cifs/cifsfs.c | 21 ++++++++++++++++++++- > fs/cifs/inode.c | 5 ----- > 2 files changed, 20 insertions(+), 6 deletions(-) Good catch. I was also able to reproduce it with CONFIG_KASAN=y when running xfstests generic/011 multiple times. > diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c > index d0b9fec111aa..bb9592594fcc 100644 > --- a/fs/cifs/cifsfs.c > +++ b/fs/cifs/cifsfs.c > @@ -1143,8 +1143,27 @@ const struct inode_operations cifs_file_inode_ops = { > .fiemap = cifs_fiemap, > }; > > +const char *cifs_get_link(struct dentry *dentry, struct inode *inode, > + struct delayed_call *done) > +{ Aren't you supposed to return ERR_PTR(-ECHILD) when !dentry (e.g. rcu-walk mode)? > + char *target_path = NULL; > + > + spin_lock(&inode->i_lock); > + if (likely(CIFS_I(inode)->symlink_target)) > + target_path = kstrdup(CIFS_I(inode)->symlink_target, > + GFP_ATOMIC); > + spin_unlock(&inode->i_lock); Can't you get rid of above kmalloc() inside spin lock and do something like target_path = kmalloc(PATH_MAX, GFP_KERNEL); if (!target_path) return ERR_PTR(-ENOMEM); spin_lock(&inode->i_lock); if (likely(CIFS_I(inode)->symlink_target)) strscpy(target_path, CIFS_I(inode)->symlink_target, PATH_MAX); else { kfree(target_path); target_path = ERR_PTR(-EOPNOTSUPP); } spin_unlock(&inode->i_lock); if (!IS_ERR(target_path)) set_delayed_call(done, kfree_link, target_path); return target_path;